What Is Pulmonary Embolism?

Pulmonary embolism (PULL-mun-ary EM-bo-lizm), or PE, is a sudden blockage in a lung artery. The blockage usually is caused by a blood clot that travels to the lung from a vein in the leg.

A clot that forms in one part of the body and travels in the bloodstream to another part of the body is called an embolus (EM-bo-lus).

PE is a serious condition that can:

Damage part of your lung because of a lack of blood flow to your lung tissue. This damage may lead to pulmonary hypertension (increased pressure in the pulmonary arteries).

Cause low oxygen levels in your blood.

Damage other organs in your body because of a lack of oxygen.

If a blood clot is large, or if there are many clots, PE can cause death.

Overview

PE most often is a complication of a condition called deep vein thrombosis (DVT). In DVT, blood clots form in the deep veins of the body—most often in the legs. These clots can break free, travel through the bloodstream to the lungs, and block an artery.

Deep vein clots are not like clots in veins close to the skin's surface. Those clots remain in place and do not cause PE.

Outlook

The exact number of people affected by DVT and PE isn't known. Estimates suggest these conditions affect 300,000 to 600,000 people in the United States each year.

If left untreated, about 30 percent of patients who have PE will die. Most of those who die do so within the first few hours of the event.

The good news is that a prompt diagnosis and proper treatment can save lives and help prevent the complications of PE.